The majority of inks and toners used in the printing industry employ water insoluble polymers for print adhesion and durability. Water-based inks, such as used in ink-jet printing, can incorporate water insoluble polymer as dispersed particulates. The particulates are typically designed with a glass transition temperature (Tg) near room temperature to allow formation of a print-film on the printed substrate under normal ambient conditions.
The thermal ink-jet printing process presents a significant challenge to polymer particle-based inks since the ink is jetted under high fluidic shear at temperatures that are significantly above the Tg of the particle. Thermal ink-jet printing is rather unique in requiring a polymer solid to operate above its Tg. Conversely, most other polymer solid applications typically only require performance below the Tg of the solid. Under the elevated temperature conditions of a thermal ink-jet pen, conventional polymer particles produce severely degraded print and pen performance. This degradation typically includes reduced jet drop velocity, drop weight and attainable drop frequency (print speed), and clogged pen nozzles and ink channels. Thus, there exists a need, therefore, for polymer particles for use in ink-jet inks that provide improved print performance at elevated temperatures such as are produced by thermal ink-jet pens.